Field of the Invention
The present invention relates to a machining control device, and particularly to a machining control device configured to control the rotational speed of a spindle to which a tool for cutting a workpiece is attached and a machine tool provided with the same.
Background Information
For example, in boring a workpiece with a milling tool, the tool is required to have a long length for avoiding spatial interference between the tool and the workpiece. In such a tool, a distance becomes long between a blade part and a part chucked by a spindle, and thereby, the stiffness of the tool becomes relatively weak.
Now, when an undulation is left uncut on a workpiece in the previous cutting step, the tool in a cutting motion is configured to be shifted and cut the workpiece along a target profile in the next cutting step. In this case, the cutting thickness is supposed to vary. In such a cutting process, where the stiffness of the tool is weak as described above, variation in cutting force excites normal mode of the tool, and thereby, chatter vibrations come to easily occur during the cutting process.
In view of this, in a well-known cutting process, a machining condition under which chatter vibrations do not occur is found out by executing a trial machining operation a plurality of times, and an optimal machining condition is configured to be set in accordance therewith.
Further, as described in Japan Laid-open Patent Application Publication No. JP-A-2007-167980, a method has been also proposed that chatter vibrations are predicted using a stability limit curve and a machining condition is set in accordance therewith. In the method described in Patent Literature 1, a parameter such as a cutting force characteristic value, determined based on a tool specification and a workpiece material, is set as an input value. In accordance with the input value, an initial value is set for a stability limit cutting-in amount so that chatter vibrations do not occur. Further, comparison is executed between the initial value and a value calculated based on the initial value, and the initial value is modified based on the result of comparison. The aforementioned processing is repeated, and the stability limit cutting-in amount is determined when an error between the modified initial value and the calculated value falls within a predetermined range.